I've been trying to find a good starting point for a home grown digtial decoder. My basic plan is to take an exsiting unit and replace the DAC with spdif outputs for each channel pair . I'm then going to feed these into exsiting wadia DAC's that I have.

I picked up a Technics AC500d which i thought would be a good starting point based on reviews. However my initial lisiting tests have me worried that its decoding is not up to the job.

I built a simple cs8402 based spdif interface and connected it to the DAC (cs8401) l/r outputs. It works however when i A/B test it against a recent okyo decoder it sounds very very poor. No high frequency and limited bass.

I'm starting to think that the quility of the decoding software is not great and therfore I was thinking about giving a Rotel RDA975 a try. Does anyone have an experince with these decoders? Anyone else had any luck making them work in this configuration?

I have the Technics, and find it ok for surround & DTS, but as a 2ch DAC, it is almost useless...
Some improvements I have done:
OpAmp (IC451 & IC452) is main ch. Try OPA2406.
IC453 is for SUB, not critical, IC501 & IC552 is SUB, Center LS & RS, I used OPA4134.
There is a lot of DC-blocking caps; L & R; C453+C454+C461+C462,
C.ch; C503+C505+C509+C515,
LS+RS ch; C553+C554+C555+C556+C559+C560+C565+C566,
try swapping with bi-polar 10uF/16-25V....
I felt that some more gain would help, and fixed it by swapping R453+R454(8,2K) with 4,7 or 5,6K (can't remember exactly...).